Preheat your oven to 160 degrees and line the base and sides of a 20cm square baking tin with baking paper - this will help you to remove the brownies once they are cooked.
In a large saucepan (you want it to be big enough to add the extra ingredients to later), melt the butter, cocoa and sugar over a low heat – stirring continuously.
Add the vanilla essence and egg - whisking the mixture as you go.
Sift the flour over the mixture and whisk to combine.
Spoon half the mixture into the cake tin and carefully place 9 Peanut Butter Cups on top.
Cut the remaining Peanut Butter Cups into large chunks.
Add the remaining brownie mixture to cover the Peanut Butter Cups and sprinkle the cut pieces over the top before placing into the oven to bake for 35 minutes.
Allow Brownie to cool in the tin before removing, cut into small pieces - or large pieces - there's not judgement here!